The present invention relates to a controlling apparatus of a motor, for example, a synchronous motor as a power source of an electromobile, and more particularly to a controlling apparatus intended for a fail-safe operation in case of a failure of an encoder detecting the rotation of the motor.
The development of electromobiles has been rapidly progressed from the viewpoint of countermeasures against environmental problems, and the power source of an increased number of the recent electromobiles has been replaced with an alternating current motor from a direct current motor because of its advantageous points such as maintenance easiness and the like. Particularly, a synchronous motor using a magnet as a rotor is highly efficient, and therefore eagerly fitted for use in the electromobiles. While the synchronous motor of this kind has conventionally been widely used in the factory automation or industrial field, the basic controlling system of the synchronous motor used in electromobiles is almost the same as in the factory automation or industrial usage. However, because of the undeniable fact that human lives are exposed to a high risk in vehicles, it is necessary to take all possible fail-safe measures.
In the electromobiles, when an output of an accelerator sensor interlocking with an accelerator pedal, that is, a signal of the accelerator sensor increasing, e.g., linearly corresponding to the opening degree of the accelerator, and an output signal of an encoder showing the current rotating speed of a motor and the position of a rotor, etc. are inputted to a control device, the control device detects the difference of a speed command signal which is the accelerator sensor signal and a current speed signal which is the output signal of the encoder, thereby controlling to supply a torque current corresponding to the above difference to the motor. At the same time, a voltage to feed the torque current is written beforehand in a ROM or the like in the form of data of the driving waveform (for instance, sine waves) of the motor. The data of the waveform is read out from the ROM or the like in correspondence to the position of the rotor, then D/A converted and supplied to the motor via a PWM inverter in association with the rotation of the rotor. This is a general controlling system of the electromobiles.
In the above-described arrangement, however, if the encoder fails, it is impossible to form a suitable voltage waveform of the motor corresponding to the rotation of the rotor, and therefore impossible to rotate the motor normally.